In the following description, a case in which the wireless communication system includes abase station and a user terminal is described as an example. In this example, a link from the base station to the user terminal, and a link from the user terminal to the base station are referred to as a downlink and an uplink, respectively. A transmission signal from the base station to the user terminal and a transmission signal from the user terminal to the base station are referred to as a downlink signal and an uplink signal, respectively.
Recently, a protocol of the wireless communication system referred to as 3rd generation (3G) is widely adopted.
Japanese Laid-Open Patent Publication No. 2007-124682 discusses the packet communication of the wireless communication apparatus in which the transmission entity receives the feedback message from the reception entity of the communication destination, and transmits the retransmission data packet when the reception is not successful. The reception entity of the communication destination performs soft synthesis of the previously received packet and the retransmitted packet.
The 3G has some stages in development, and a portable phone adopting a protocol referred to as 3.5G or a High-Speed Downlink Packet Access (HSDPA) with further higher communication speed in addition to an original 3G adopted in FOMA™ or the like appears, and further, the protocol referred to as Super3G or 3.9G is considered. The protocol in the wireless communication system of the 3G group is divided into a plurality of layers, and a layer 1 thereof is a layer referred to as a physical layer, and this is a part that assumes actual communication.
A layer 2 is formed in a superior portion of the layer 1. This layer 2 is formed of three sub-layers. The three sub-layers are a Medium Access Control (MAC), a Radio Link Control protocol (RLC), and a Packet-Data Convergence Protocol (PDCP). FIG. 1 illustrates a configuration diagram of the layer 2 of the Super3G protocol. PDCP entities and RLC entities as many as the number of Logical Channels (LCH) to be used are formed. Each LCH transmits and receives each Protocol Data Unit (PDU). A MAC entity allocates resource to each RLC entity. Also, the MAC entity binds RLC-PDU transferred from each RLC entity to one PDU by multiplexing, and transfers the PDU to a Hybrid Automatic Repeat-reQuest (HARQ) processing unit. The HARQ processing unit uses Stop&Wait for performing retransmission control by Acknowledgement/Negative Acknowledgement (ACK/NACK) to perform retransmission control in order to perform retransmission for a PDU retransmission request from the receiving side. Herein, one block of processing functions arranged in one layer or one sub-layer is referred to as an entity.
In the Super3G protocol, the signal relating to the above-described retransmission control and an operation on the receiving side (UE: User Equipment) or the like are illustrated in FIGS. 2A and 2B.
FIG. 2A is a view illustrating a name of channel to be used by the signal, a name of signal, a link indicating in which of the uplink and downlink the signal is used, existence or nonexistence of Cyclic Redundancy Check (CRC) protection, a transmission timing at which the signal is transmitted, information, which each signal has regarding the HARQ, and contents of the information. FIG. 2B is a view illustrating information contents when detecting Physical Hybrid ARQ Indicator Channel (PHICH) and Physical Uplink Control Channel (PUCCH) and when detecting Physical Downlink Control Channel (PDCCH), which are signals (represented by channel names) in FIG. 2A, on the UE side, and the operation on the UE side based on the signals. For example, when the UE obtains ACK information in the PHICH and obtains transmission information in the PDCCH, which is the combination No. 1 in FIG. 2B, the PDU next to the previously transmitted PDU is transmitted by the UE side based on the PDCCH.
As illustrated in FIG. 2A, the retransmission request signals performed by the retransmission control by the HARQ processing unit in the uplink and in the downlink are different from each other. In a case of the uplink, error correction process and CRC data are added to the data to be transmitted to the base station to perform the transmission process. The HARQ processing unit on an opposing side (that is to say, the base station side) returns NACK information to the opposing side (that is to say, the user terminal side) when the reception information indicates reception NG (CRC NG: that is to say, when it is determined that the data is incorrect as a result of check using the CRC information). The HARQ processing unit transmits the ACK information to the opposing side (user terminal side) when the reception information indicates reception OK (CRC OK: that is to say, when it is determined that the data is correct as the result of the check using the CRC information).
FIG. 3 is a view illustrating the communication between the conventional user terminal and base station and each operation. FIG. 3 is a view more illustrating a case in which data to be sequentially transmitted such as data #1 and data #2 are on the user terminal side. In FIG. 3, HARQ Pr#A and the like are obtained by separating transition in time in the communication between the user terminal and the base station in process units. First, the data #1 is transmitted from the user terminal side, and this data #1 is received by the base station side through AIR. When reception error occurs at the time of receiving the data #1, the base station side notifies the user terminal side of the NACK information and retransmission information by an HARQ reception result signal and a transmission resource notifying signal using the PHICH and the PDCCH (corresponding to a combination No. 4 in FIG. 2B). The user terminal side transmits again the data #1 to the base station side, according to the retransmission information. By the retransmission, when the data #1 is normally received by the base station side, the base station side notifies the user terminal side of the ACK information and the transmission information by the HARQ reception result signal and the transmission resource notifying signal (corresponding to the combination No. 1 in FIG. 2B). The user terminal side transmits new data #2 to the base station side according to the transmission information.
FIG. 4 is a view illustrating communication between the conventional user terminal and base station and each operation. This is different from the example illustrated in FIG. 3 in that this is a case in which only the ACK information and the NACK information are transmitted, the transmission resource notifying signal is not transmitted from the base station side, and there is no data to be transmitted next to the data #1 on the user terminal side. As in the case illustrated in FIG. 3, when the reception error occurs at the time of receiving the data #1 on the base station side, the NACK information is transmitted from the base station side to the user terminal side. Herein, since the transmission resource notifying signal protected by the CRC is not added, the user terminal side retransmits the data #1 based on the NACK information. When the base station side normally receives the data #1, the data #1 is passed to a superior processing unit. On the other hand, the ACK information is transmitted to the user terminal side so as to notify the normal reception, and the user terminal side holds the transmitted data #1 without retransmitting the same.
FIG. 5 is a view illustrating the communication between the conventional user terminal and base station and each operation. FIG. 5 is a view more illustrating a case in which the data #1 is transmitted from the base station side to the user terminal side. In this case also, when the reception error occurs to the data #1 from the base station side, the user terminal transmits the NACK information to the base station. The base station side retransmits the data #1 according to the NACK information, and when the NACK information is normally received by the user terminal side, the user terminal side transmits the ACK information to the base station side (refer to FIG. 2A, PUCCH), and the base station side holds the transmitted data #1 without retransmitting the same.
As described above, in a case that the data to be transmitted still remains in the user terminal or the base station on the transmitting side and it is possible to allocate the data to the resource (size of the MAC PDU), the transmission resource notifying signal is transmitted to the user terminal side. The transmission resource notifying signal is protected by a CRC code, and reliability thereof is higher than that of the ACK signal and the NACK signal, which are the HARQ reception result signals described above. The base station side adds the transmission information to the transmission resource notifying signal when reception is OK and a new PDU is requested to the user terminal side. The base station side adds the retransmission information to the transmission resource notifying signals and transmits the signals to the user terminal side when retransmission is requested to the user terminal side (refer to drawing illustrating signal in FIG. 2, and refer to FIG. 3).
When the user terminal or the base station on the transmitting side receives only the signal from the PHICH, the user terminal or the base station on the transmitting side retransmits the object PDU to the base station side when the signal is the NACK information, and saves the data without retransmission the same when this is the ACK information (refer to FIG. 4).
When the transmission side receives the signal from the PHICH and the PDCCH, based on the information of the highly reliable PDCCH, in a case that a transmission resource signal is the retransmission information, the retransmission of the object PDU is performed, and in a case that this is the transmission information, the transmission of the new PDU is performed (refer to No. 1 to No. 4 in FIG. 2B and FIG. 3).
Although an operation in the downlink is substantially the same with that of the uplink, there is no signal protected by the CRC corresponding to the transmission resource notifying signal, so that the request of the new PDU and the retransmission request are performed only with the HARQ reception result signal.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2007-124682
As described above, since the HARQ reception result signal transmitted from the receiving side to the opposing side is not protected by the CRC and a check bit, the ACK information transmitted from the receiving side might change to the NACK information, and on the other hand, the NACK information might change to the ACK information due to the effect of the noise or the like. In a case of the uplink, when there is still the data to be transmitted in the UE (transmitting side) and it is possible to allocate the resource, it is possible to transmit the transmission resource notifying signal protected by the CRC, and correctly determine whether this is the request of the new PDU or the retransmission of the PDU by the transmission information and the retransmission information included in the signal. However, when the HARQ reception result signal is not protected and the NACK information changes to the ACK information, the user terminal or the base station on the receiving side may not correctly receive the NACK information, so that the user terminal or the base station on the transmitting side, which determines that the ACK information is received, does not perform the retransmission even though the retransmission request is transmitted. Therefore, in the user terminal or the base station on the transmitting side, which transmits the NACK information, the MAC processing unit cannot receive the PDU data, and the retransmission is not performed until the retransmission request is transmitted by the retransmission control by the RLC entity, which is in a superior portion of the MAC entity.
This process is described in more detail with reference to FIG. 6. This example illustrates a case in which there is no data to be transmitted next to the data #1. When the data #1 is transmitted from the user terminal side to the base station side, in a case that the reception error occurs to data #1, the NACK information is transmitted from the base station side to the user terminal side. The transmission data changes before the NACK information reaches the user terminal side (indicated as error), and when the transmission data is received as the ACK information by the user terminal side, the user terminal side recognizes that the transmitted data #1 is normally received on the base station side, and there is no Grant signal (for example, the transmission signal and the Retransmission signal), so that the user terminal side does not perform the transmission and stands by while holding the data #1. On the other hand, on the base station side, even though the NACK information is transmitted, the data #1 is not retransmitted.